Pulmonary emphysema has been clinically and experimentally associated with a progressive degradation of alveolar elastic fibers. Over the last several decades numerous animal models have been developed to study emphysema. Many of those models target the degradation of pulmonary interstitial elastic fibers through administration (intratracheal instillation or aerosol inhalation) of proteolytic enzymes capable of digesting elastin. The enzyme-treated animal models have provided evidence for entry of the administered elastase into the lung interstitium and the subsequent degradation and loss of elastin. Long term studies have revealed that when elastin degradation slows, resynthesis of elastin occurs to eventually reinstate initial levels of insoluble elastin. This resynthesis, however, is not effective in restoring structural or physiological damage. Although animal models have provided significant biochemical, morphological and physiological data relevant to pathological mechanisms and clinical impact, little is known of specific cellular or underlying molecular responses. Attempts to investigate specific cell responses to elastin injury within a controlled environment are very difficult with whole tissue studies. Organ culture, although allowing a targeted and controlled environment, suffers in the necessarily short-term duration of the experiments as well as cellular heterogeneity present. The underlying hypothesis of this application is that there exists a normal repair response to interstitial lung elastic Tiber degradation (injury). Initiation and progression of emphysema involves an imbalance in the injury-repair homeostasis such that injury (degradation) is predominant and repair mechanisms are inoperative or ineffective. We propose to test this hypothesis in cultures of pulmonary fibroblasts. The aims of the proposal are to first develop optimum conditions for observing maximum cell response to leukocytic elastase digestion and digestion products. Once established, the level of response (transcriptional, post-transcriptional, translational, and post-translational) will be examined by molecular biological and biochemical techniques. The peptide signal(s) responsible will be characterized both in terms of the peptide(s) origin and primary structure. The possible existence of cell receptors for specific peptides will be investigated. The insoluble cell matrix will also be examined for its possible role in potentiating cell response. Lastly, specific mechanisms of active peptides on both up and down regulation of tropoelastin mRNA steady- state levels will be explored by focusing on interactions between peptide and mRNA to regulate translatability and stability, and peptide and DNA to regulate transcription. The experimental approaches proposed integrate technologies of molecular and cell biology, immunology and biochemistry.